A source heard Prince Charles express opposition to the policy several times in private, and that he was “more than disappointed” by it, according to The Times.
The comments were reported after a High Court ruling paved the way for the first flight to the east African country to go ahead on Tuesday.
A Clarence House spokesman said: “We would not comment on supposed anonymous private conversations with the Prince of Wales, except to restate that he remains politically neutral. Matters of policy are decisions for government.”
As head of state, Charles’s mother the Queen has to remain strictly neutral with respect to political matters and does not vote or stand for election, the royal family’s official website says.
Traditionally, royals do not become involved in political matters.
However Charles, a future king, has been outspoken in the past and faced criticism over his involvement in public and political issues.
In 2015, Charles had to defend his decision to write a series of letters to government ministers, some of which became known as the “black spider” memos, so-called because of his use of black ink.
At the time, Clarence House said the correspondence – on issues including a lack of resources for armed forces fighting in Iraq, the benefits of complementary medicine, and the need for affordable rural homes – showed “the range of the Prince of Wales’s concerns and interests for this country and the wider world”.
In the same year there was controversy when it emerged Charles had been routinely receiving copies of confidential Cabinet papers for more than 20 years.
As well as the Queen, it included the Prince of Wales, although it was not suggested he had requested access. Heirs to the throne were believed to have been included in the group since the 1930s.
In a BBC documentary to mark his 70th birthday in 2018, Charles said he would stop speaking out on issues when he became king, saying he was “not that stupid” to continue what some had termed “meddling”.
The prince acknowledged he would not be “able to do the same things I’ve done as heir”, and as monarch would have to operate within “constitutional parameters”.
In 2020, Buckingham Palace appeared to distance itself from comments made by Charles’s son, the Duke of Sussex, as Harry urged people in the US to “reject hate speech” and vote in the presidential elections.
Harry faced a backlash amid claims of political interference and suggestions he was telling people to vote against Donald Trump.
Although UK law does not ban royalty from voting, it is considered unconstitutional for them to do so.
Buckingham Palace highlighted the fact Harry was no longer a working royal, and said his remarks were made in a “personal capacity”.